The objectives of this investigation are to establish conditions for the maintenance of rodent lung in vitro as an organ explant and to employ this organ culture model to study the regulation of dipalmitoylphosphatidylcholine (DPPC) synthesis, storage and secretion as it relates to the "surfactant system" of the lung. Explants of lung tissue from adult and fetal rats will be placed in HAM's F12K culture medium. Evaluation of variables associated with organ culture will be made, for example, hormones, vitamins, special nutrients. Tissue in culture will be evaluated histologically by light and electron microscopy. Biochemical assessment of tissue viability will include glucose conversion to CO2 and lactic acid as well as glucose, glycerol choline and acetate conversion to lipids. Detailed studies on the ability of lung in culture to synthesize DPPC and the regulatory aspects of this synthesis will be investigated by radioisotope techniques and specific enzyme analysis. Embryonic lung explants will be studied in terms of their ability to continue differentiation in vitro and to become capable of DPPC synthesis and "surfactant" production.